Off Grid Hydro Power 101

HydroGenMicro-hydroelectric generators are yet another method of producing electricity off the grid.

If you are blessed with a suitable creek, hydro is definitely something you should look into. This is particularly true if your area of the country experiences long periods of very cloudy weather (thereby making solar more expensive and more difficult to use year- round).

Hydro power has some major advantages and some disadvantages. In this article, I'll help you discover if the pros outweigh the cons in your situation, because it's different for everyone.  Much of it will depend on the details of your creek, power system, climate, the lay of your land, and your mechanical abilities.

Turbines

There are two main types of micro-hydro generators, impulse turbines and reaction turbines. Impulse turbines are the most common because they require far less water volume than reaction turbines, and most people who own a creek do not have sufficient volume to power a reaction turbine. So we will focus primarily on impulse turbines.

How It Works

Micro-hydro works on the principle of gravity exerting pressure on water as it is stacked on top of itself. Think of swimming in a deep pool of water. Now dive down to the bottom. Notice how your ears feel stopped up and then pop? This is due to the pressure of all that water above you. This same effect happens when we channel water into a pipe and run the pipe downhill some distance. It is all based on how many vertical feet uphill we can capture the water. In a pool, the deeper you dive, more water is above you, and more pressure is exerted on your body. The same principle applies here. The higher we capture that water in our pipe, and the further downhill our hydro generator is, the more “head” our system has.

“Head” is a term that simply refers to the number of feet of vertical fall from the top of our pipeline down to the hydro unit. So 30 feet of fall would be 30 feet of head. The more head we have, the more pressure is produced down at the bottom, where our hydro generator is. Please note that we are referring to the number of vertical feet, not how long the pipe is (the pipe may be 300 feet long but may only fall 20 vertical feet). For every one foot of head, .43 pounds per square inch (PSI) of pressure is produced. So 100 feet of head would produce around 43 PSI. Likewise, if you were to go scuba diving and descend down to 100 feet below the surface, approximately 43 PSI of pressure would be exerted on your body.

So with all this pressure at the bottom of our pipeline, we can force the water into a small jet that has the same effect as placing your finger over the end of a garden hose--it increases the velocity of the water. The water shooting out of the jet is now directed against a small wheel with specially designed blades (kind of like spoons) that spins around as the water hits it. This wheel turns an alternator which produces electricity. This electricity is sent to the battery bank and stored there.

Advantages of Hydro

  • Unlike solar or wind, hydro runs 24/7, as long as the creek is flowing sufficiently. So even a small amount of power can add up to quite a substantial quantity when it is operating continuously.
  • Hydro is not dependent on the weather. As long as the creek is reliable, it keeps charging the batteries--sun or no sun, wind or no wind.
  • Even if the creek dries up during summer months, hydro still offers a source of generating power during those dark winter months (so it is an excellent companion to solar).
  • Hydro is often easier on batteries because they do not tend to become discharged as deeply as with a solar system (of course, this depends on the particulars of your system).
  • Also, a good hydro system is typically less expensive than a comparable solar system (less expensive components and usually requires fewer batteries).

Disadvantages of Hydro

  • Probably the largest drawback to hydro is the creek. While it certainly is possible to find property with a suitable creek, most properties do not have such a treasure. And even if a property does have a creek, that does not guarantee it is a suitable one for hydro.
  • Property with a creek will almost always be significantly more expensive than a comparable parcel without (this could more than make up for the lower initial cost of a hydro system).
  • Hydro is not the nearly maintenance-free solution that solar is. It needs to be maintained (i.e. filters checked, etc.) and the operator needs to keep an eye on it.
  • And, depending on the lay of the land, installing the hydro system can be much more labor intensive (or expensive if hiring someone else) than a comparable solar system.

Checking the Site

There are two main factors that determine the potential of a micro-hydro site.

  1. The amount of head (in feet) and
  2. The amount of water flow (gallons per minute).

These are the two most important factors for determining the suitability of a site.

A quick and easy formula for determining if a site is even worth considering is:

Head (Feet) x Flow (GPM) / 13 = Power Produced (Watts)

In other words, the number of feet of head times the number of gallons per minute divided by 13 equals a rough estimate of how many watts could potentially be produced (if properly designed and installed). An example:

  • 50 (feet of head) x 100 (GPM) / 13 = 384 (watts)

If the formula yields close to 50 watts or more, then definitely look into it more thoroughly.

Remember, this is only a very rough formula for determining if the site is even worth looking at. You will need to do a more detailed analysis later on if the decision is made to move forward with hydro.

But as you can see, the example above could be an excellent candidate for hydro. Roughly 384 watts times 24 hours in a day equals 9,216 watt hours per day, or 9.2 kWh per day! Based on our energy usage, we could power three identical homes with that one hydro unit!

Even much smaller amounts of power may be worth developing. A site with 20 feet of head and 50 GPM flow could yield somewhere around 76 watts. For the entire day, that could yield 1,824 watt hours. That is almost enough to power our home. With some solar added in, you could be very nicely set up. Even 15 feet of head and 40 gallons per minute would take care of half our power needs. That would be a huge blessing in the winter!

Even much less volume can work if there is enough head. For instance, only 10 gallons per minute with 80 feet of head could produce somewhere in the neighborhood of 61 watts, or over 1,400 watt hours!

Micro Hydro Generator Models

Here's a list of what I consider to be some of the better micro hydro options.  It is not exhaustive, but should plug you into most of the better options.

More info?

This is just a brief introduction to the fascinating topic micro hydro power.  Are you looking for more details?  Make sure you are subscribed to our free email training newsletter (subscribe at the top right of this page).  Also, keep an eye out for the next Off Grid Boot Camp class, where you can gain a thorough understanding of how to choose, use, and maintain and off grid power system.

5 Comments

  • Avatar

    Oscar Gunn

    Reply Reply July 28, 2015

    Bro. Meissner, my family and I were blessed to get a home that we can fix up in Tenn. We have 10 acres,with a nice creek that runs thru it and a s poo ring fed pond. There is also a barn and some smoke houses. We've been in the city for a longtime and now we have an opportunity to do things God's way. Our creek runs pretty strong, so I'm definitely interested in the hydro power.

  • Avatar

    Peter McPherson

    Reply Reply June 21, 2017

    For those of us who don't live in the US, could you give us your formula Head (Feet) x Flow (GPM) / 13 = Power Produced (Watts)in metric units?

    • Avatar

      Bob Gaar

      Reply Reply November 21, 2017

      Try meters X liters/minute divided by 15 = watts

      • Avatar

        Peter McPherson

        Reply Reply November 21, 2017

        Thanks Bob.

  • Avatar

    Ken

    Reply Reply June 22, 2017

    In your list of equipment, do not leave out the Scott turbine of Republic, WA.
    It is a good quality low head unit.
    It is a reaction turbine (cross flow) for those who have a good flow but small head.

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